Heat-insulating structures and heat-insulating coatings, i.e. thermal barrier coatings have been employed by those skilled in the art to enhance the thermal efficiency of internal combustion engines by permitting more complete fuel burning at higher temperatures. Typically, such heat-insulating coatings have been applied to all of the chamber surfaces, including the cylinder wall and head and piston combustion face to prevent heat loss.
Heat-insulating structures and heat-insulating coatings have also been used in automobile exhaust systems to maintain high exhaust temperatures required by thermal reactors and catalytic converters and impede the emission of unburned hydrocarbons emitted into the atmosphere as an undesirable component of exhaust gas.
In previous attempts to increase thermal efficiency, heat-insulating structures and heat-insulating coatings such as ceramic plates and ceramic coatings, respectively, have been applied to component surfaces. Significantly, such ceramic coatings function not only as heat insulation barriers but also exhibit advantageous physical characteristics such as providing a hard, corrosive resistant, and abrasive resistant surface.
Typical of ceramic materials commercially available include a cerium-yttrium zirconium oxide material as described in U.S. Pat. No. 4,599,270, available the Perkin-Elmer Corporation.
The above ceramic materials were developed principally for application to high speed turbine blades, such as used in commercial aircraft, turbo engines. Typically, these blades are made of nickel-based superalloy, high strength steel materials and environment is one in which the blades, thus the ceramic lining on the blades, is subjected to high temperatures at relatively constant, non-cyclical, compressive loads.
Prior art literature describing the use of ceramic materials for these applications and techniques for applying the ceramic lining are shown in more detail in U.S. Pat. Nos. 4,273,824; 4,332,618; 4,335,190; 4,880,614; and 4,916,022.
The need or demand for such a heat insulating barrier in internal combustion engines, and particularly two and four cycle compression-ignition (diesel) engines, has only recently come to be realized. Recent engine designs, and the modification of pre-existing engine designs, has included increasing the power output demands for a cubic inch displacement of the engine's power capacity. Such designs have resulted in higher compression ratios and exhaust gas temperatures. Not only is it important to keep the exhaust gas temperatures from reaching the cylinder head and related components, thus reducing the cooling requirements and other engine design requirements, the heat of the exhaust gas is being used to increase the engine efficiency by recirculating it through the intake air ports.
However, experience has shown that the ceramic coatings and techniques for application to apparatus such as gas turbine engine blades, previously referenced, is not ideal for application to the surfaces of combustion chamber components in compression-ignition internal combustion engines, where (i) the substrate materials including the cylinder head and piston may be cast iron, (ii) the materials of the related components such as the exhaust valves may be aluminum alloyed high temperature steel or metallic based alloy, and (iii) the temperatures in the combustion chamber and at the combustion chamber surfaces are extremely high.
Previously known ceramic coatings and techniques for depositing the same are even less ideal for 2-cycle compression-ignition internal combustion engines such as applicant's Series 149 engine which utilizes a pot-type cast iron cylinder head. In applicants' Series 149 engine design, the temperatures in the combustion chamber are even greater than in conventional internal combustion engines, since every stroke of the piston is a combustion stroke. For example, temperatures in the combustion chamber may vary between 150.degree. to 1400.degree.. Similarly, temperatures at the combustion chamber surfaces cyclically range from about 150.degree. when being freshly charged with intake air to about 1500.degree. at combustion. All of these factors contribute to the requirement for new materials and techniques in accordance with the present invention.
Prior disclosures include those shown in U.S. Pat. Nos. 3,911,890, 3,976,809 and 3,911,891 for coating piston heads and U.S. Pat. No. 4,077,637 for coating piston rings, as well as U.S. Pat. No. 4,254,621 for ceramically coating any of the combustion chamber surfaces including the cylinder head. However, none of these is considered to serve the purposes of the present invention in providing an extremely cost effective and efficient dual layer ceramic lining and application technique for lining the combustion chamber surfaces of a compression-ignition internal combustion engine expanded to the above-mentioned operating conditions.